Hoechst 34580 is a good candidate for treating Alzheimer's disease by inhibiting Aβ formation. 50 μM Aβ42 solutions co-incubated with 100, 25, 12.5, 3.125, 0.78, and 0.1, 0.01 μM Hoechst 34580 at 37 °C for 70 h. Hoechst 34580 can inhibit the aggregation of Aβ42 in a dose-dependent manner. The IC50 is obtained by measuring the concentration of Hoechst 34580 while maintaining the Aβ42 concentration which gave 0.86±0.05 μM for Hoechst 34580.